E2-25K mediates US11-triggered retro-translocation of MHC class I heavy chains in a permeabilized cell system
| Autor: | Cecile M. Pickart, Tom A. Rapoport, Vincent Chau, Catherine S. Coleman, Dennis Flierman |
|---|---|
| Rok vydání: | 2006 |
| Předmět: |
Recombinant Fusion Proteins
Cytomegalovirus Genes MHC Class I Ubiquitin-conjugating enzyme Endoplasmic-reticulum-associated protein degradation Viral Proteins Ubiquitin Cell Line Tumor MHC class I Animals Humans chemistry.chemical_classification DNA ligase Multidisciplinary biology Endoplasmic reticulum Ubiquitin-Protein Ligases RNA-Binding Proteins Biological Sciences Cytosol Biochemistry chemistry Ubiquitin-Conjugating Enzymes biology.protein Biological Assay Cattle Immunoglobulin Heavy Chains Dimerization |
| Zdroj: | Proceedings of the National Academy of Sciences. 103:11589-11594 |
| ISSN: | 1091-6490 0027-8424 |
| Popis: | In cells expressing human cytomegalovirus US11 protein, newly synthesized MHC class I heavy chains (HCs) are rapidly dislocated from the endoplasmic reticulum (ER) and degraded in the cytosol, a process that is similar to ER-associated degradation (ERAD), the pathway used for degradation of misfolded ER proteins. US11-triggered movement of HCs into the cytosol requires polyubiquitination, but it is unknown which ubiquitin-conjugating and ubiquitin-ligase enzymes are involved. To identify the ubiquitin-conjugating enzyme (E2) required for dislocation, we used a permeabilized cell system, in which endogenous cytosol can be replaced by cow liver cytosol. By fractionating the cytosol, we show that E2-25K can serve as the sole E2 required for dislocation of HCs in vitro . Purified recombinant E2-25K, together with components that convert this E2 to the active E2-ubiquitin thiolester form, can substitute for crude cytosol. E2-25K cannot be replaced by the conjugating enzymes HsUbc7/Ube2G2 or Ube2G1, even though HsUbc7/Ube2G2 and its yeast homolog Ubc7p are known to participate in ERAD. The activity of E2-25K, as measured by ubiquitin dimer formation, is strikingly enhanced when added to permeabilized cells, likely by membrane-bound ubiquitin protein ligases. To identify these ligases, we tested RING domains of various ligases for their activation of E2-25K in vitro . We found that RING domains of gp78/AMFR, a ligase previously implicated in ERAD, and MARCHVII/axotrophin, a ligase of unknown function, greatly enhanced the activity of E2-25K. We conclude that in permeabilized, US11-expressing cells polyubiquitination of the HC substrate can be catalyzed by E2-25K, perhaps in cooperation with the ligase MARCHVII/axotrophin. |
| Databáze: | OpenAIRE |
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